This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.
Specific Aims : Rationale: Peripheral arterial disease (PAD) is a leading cause of morbidity due to ambulatory limitations associated with intermittent claudication.1-4 Intermittent claudication is ischemic muscular pain that occurs in the calf, thigh, or buttock muscle groups during ambulation when the pace exceeds the capacity of the peripheral circulation to adequately perfuse the active lower extremity musculature. Intermittent claudication afflicts 5% of the US population older than 55 years of age, 5 thereby limiting daily physical activities6 and negatively affecting quality of life7 in many older adults. Because ambulation is one of the primary physical activities performed by the elderly,8 it is not surprising that PAD subjects adopt a sedentary lifestyle and typically cluster around the extreme low end of the physical activity spectrum.9 The ambulatory dysfunction and sedentary lifestyle in subjects with PAD may trigger a decline in other domains of physical function. For example, PAD subjects have reduced strength in the lower extremities,10 impaired balance and higher prevalence of falling,11 altered gait even before claudication pain occurs,12 worse self-perceived ambulatory function,13 and lower health-related quality of life14 than non-PAD controls. Consequently, PAD subjects have difficulty completing activities of daily living that utilize the lower extremities,13 while some subjects are unable to perform these tasks altogether. A primary therapeutic goal for PAD patients with intermittent claudication is to regain lost physical function through exercise rehabilitation.15 Medically supervised exercise programs have been studied extensively over the past 35 years, and are efficacious in the clinical management of intermittent claudication.16 Specifically, supervised exercise rehabilitation improves initial claudication distance (ICD) and absolute claudication distance (ACD) during a standardized treadmill test, as well as overground ambulatory function, perceived ambulatory function, physical activity level, quality of life, and calf blood flow in PAD patients with intermittent claudication.16-24 Consequently, exercise-mediated improvement in claudication pain is a triggering event that breaks the downward spiraling chain of events in physical function in PAD patients. Supervised exercise programs are considered the standard method to rehabilitate PAD patients with intermittent claudication, and are efficacious in improving claudication distances measured during standardized treadmill protocols,16 as well as general ambulatory function and quality of life.18,22 Unfortunately, only a small percentage of eligible patients can feasibly attend hospital-based programs on a regular basis, thereby limiting the generalizability of the research findings. The overwhelming majority of PAD patients could, however, benefit from an exercise program transported to the community setting (i.e., home-based walking). However, few studies have been published on home exercise programs for PAD patients with intermittent claudication, none have used a randomized, controlled trial design, most have suffered from small sample sizes, and most have narrowly focused on PAD-specific outcomes such as claudication distances during a treadmill test without considering the impact of the exercise program on more general measures of physical function and overall health-related quality of life.23,25,26 In addition to these problems, the inability to accurately quantify the volume of exercise performed in home-based programs is the most serious limitation, rendering previously reported data as difficult to interpret. Recent technology using a step activity monitor can accurately record the number of steps taken in the community setting on a minute-to-minute basis for up to a month, as well as record the daily amount of time spent walking and the intensity at which the walking occurred (i.e., cadence).27 Therefore, we propose to conduct a prospective, randomized controlled clinical trial designed to address the limitations of previous home-based exercise programs, thereby allowing us to directly compare the efficacy of home-based and supervised programs to improve the functional status of PAD patients limited by intermittent claudication. Hypothesis: Ambulatory dysfunction secondary to intermittent claudication is the initial step in a downward spiral of physical function in older patients with PAD. The overall hypothesis of this project is that a home-based exercise program utilizing new physical activity monitoring technology that quantifies the volume and intensity of walking will be as equally efficacious as a standard hospital-based supervised exercise program and better than usual care control in improving ambulation, physical function, vascular function, and health-related quality of life through the physiologic mechanisms of improved walking economy, calf muscle circulation, and calf muscle oxygenation. This hypothesis will be tested in a prospective, randomized controlled clinical trial that compares a home-based exercise group, a hospital-based exercise group, and a delayed-entry, non-exercise control group to address the following three specific aims:
Specific Aim 1 : To determine the efficacy of a home-based exercise rehabilitation program to elicit improvements in outcome measures pertaining to ambulation, physical function, vascular function, and health-related quality of life.
Specific Aim #2. To compare the changes in these outcome measures in patients randomized into either a home-based exercise program, a standard hospital-based supervised exercise program, or and non-exercise usual care control group.
Specific Aim #3. To determine whether alterations in walking economy, calf muscle circulation, and calf muscle oxygenation are the primary mechanisms by which home-based and hospital-based exercise rehabilitation improve ambulation and physical function.
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